Rust removing



Patented Nov, 21, 1950 UNITED STATES PATENT OFFICE RUST REMOVING Thomas E. Burkhardt, Day on, Ohio, assignor to General Motors Corporation, Dayton, Ohio, a corporation of Delaware No Drawing. Original application September 25,

the oxide and scale. alkalinity of these solutions the workmen asso- 1940, Serial No. 358,327. Divided and this application March 28, 1947, Serial No. 738,013

This invention relates to a process for cleaning and polishing metal surfaces.

This application is a division of my cooending application S. N. 358,327 filed Se tember 25, 19 0, Patent No. 2,428,141 issued September 30, 1947.

Heretofore, highly alkaline so utions such as sodium orthosilicate solutions have been used for electrolytically cleaning metal surfaces. It was found that such processes did not p rform a sufficiently good job of cleaning and removing Also because of the h gh ciated with these processes frequent v' sufferd from skin diseases. Thesehighl 'a ka'line so utions were also objectionable since they attack the paint and enamel upon the parts to lre cleaned. Furthermore. this and similar rocesses do not lend themselves readily to automatic scae from metal surfaces which is more thorough and hich is less injurious to workmen employed thereon.

It is another obiect of mv invention to pro ide -a process of cleanin and/or remo ing oxide and sc e from metal surfaces which wil be effecti e when used in automatic conveyorized mechanized ope ation.

It is anoth r object of my invent on to provide aprocess of cleaning and/or remo ng o ideand scale from metal surfa es of artic es in which paint and e amel on the articles cleaned will not be attacked.

It is still another object of my in ention to pro ide a process of ceaning and/or removin oxide and scale from metal surfaces which will also pol sh the metal surfaces.

It is another object of my invention to provide a process for cleaning and po ishing cast iron and steel surfaces which will also remove copper therefrom.

Further obiects and advantages of the present invention will be apparent from the following description.

I have found by the use of phosphates in conjunct on with other means, such as a wetting agent, or electric current, or a suitabl acid or any combination of these, metal surfaces may be cleaned almost absolutely free of all traces of oxide and scale. Preferably my process emp'oys 2 Claims. (Cl. 252-135) an electrolyte formed of a low alkaline solution 55 having a pH value less than 10.5, preferably a. low alkaline phosphate solution such as one selected from a group consisting of tetrasodium pyrophosphate, sodium metaphosphate and sodium hexametaphosphate. This eectrolyte is kept at a fairly high temperature and the metallic surfaces to be cleaned are immersed in the electrolyte. The electrolyte is kept in agitation either by the movement of the metallic surfaces throu-h the e ectrolyte or by some other suitable means. The process may be performed either anodically or cathodically, but preferably the current is passed from the metallic surfaces as anodes to a suita le cathode in contact with the electrolyte. Toobtain more rapid action a suitable wetting agent. a suitable acid or both may be included in the electrolyte. In some cases the process may be used non-electrolytically.

As an illustration there may be used an overhead conveyor for supporting articles to be electrolytically cleaned and po ished. The articles for example, may include a-sealed unit type of compressor having cast iron and steel surfaces to be cleaned, an a uminum tray, a copper plate and a'cast iron reciprocating compressor. These are carried through an electrolyte contained in a :tank of some suitable material, such as metal or earthen ware.

The e ectrolytic bath is provided with a suitable cathode of some suitable material, such as iron "o nickeL' This cathode is connected to a source of rower for passing current from the articles as anodes through the electrolyte to the cathode.

The conve or, when in operat on, lowers the articles into the bath. connects them to thesonrce of power, and moves the articles through the bath so as to cause agitation of th eectrolytic bath adiacent the metal surface to be cleaned. Afterwards the art cles are removed from the bath and carried into rinsing tanks and other such means.

Preferably, the electrolyte comprises an aqueous solution of from 2. to 10 oz. per gallon of tetrasodium pyrophosphate. It has been found desirable to add a suitable wetting agent to the anodically, this process not only thoroughly cleans the exposed metal surfaces but it also polishes them. This action is particularly noticeable upon copper and copper alloys. Where only traces of iron oxide and rust are present upon the iron and steel surfaces, these are also thoroughly cleaned and polished in this solution. Furthermore this process may also be used for removing immersion or electro-chemical deposits of copper on iron and steel at the same time the iron and steel parts are being cleaned anodically, since th copper is removed from the, iron and steel as a part of their anodic cleaning process.

When more than traces of oxide coatings or rust are present upon iron and steel surfaces, it is desirable to use about ozper gallon of tetrasodium pyrophosphate in the electrolyte together with an amount sufficient to reduce the pH value to about 9 of an acid, such as acetic, citric, phosphoric, sulfuric, hydrochloric, nitric, and. hydrofluoric acids. This solution. may be used electrolytically or in a purely mechanical process. For still'heav'er oxide coatings, the pH value may be; further lowered by the addition of more. acid with a lower limit of 7. Likewise for lighter: oxide coatings, less acid may be used with an upper limit of 10.5. Such a solution may be used. for other metal surfaces.

Immediately following the electrolytic treatment, the. articles.- arerinsed in clean cold runningwater with cold water sprays; following this, the articles are rinsed in clean soft hot, running water ata temperature of 200 F. or more; finally, the articles are; dried by air-blasts. After drying, the parts may be coated with an oil-m;xture where-it is necessaryto prevent rusting.

If desired, the. electrolyte itself may be agitated by some other suitable means. Otherwise, themovement of the articles by the conveyor through the bath may be relied upon to. provide sufficient agitation, to remove. any polarization or similar electrical effect. It is not necessary to use the conveyor or any such means for carrying out this process.

Sodium metaphosphate and sodium hexametaphosphate have. somewhat similar properties as tetrasodium pyrophosphate and may be used in its place in substantially the same. way. Other low alkaline phosphates may also be used. However, tetrasodium p-yrophosphate is preferred.

- I find that, in using this process, certain paints and black enamel, which may be upon the articles, are not attacked. Therefore, this process may be used for painted and enameled articles which have exposed metal surfaces requiring cleaning. This is a particularly desirable advantage, since occasionally parts, after they have been pa nted or enameled, require reoperation and require cleaning of this type as a part of the reoperation procedure.

While it is desirable to maintain as set forth the specified temperatures, voltages and concentration, it is possible to use a solution of between 1 and 12 ozs. per gallon of tetrasodium pyrophosphate and to keep the temperature as low as F. Also, voltages as low as 2 to 3 volts may be used for cleaning purposes, but for cleaning and polshing it is desirable to use at least 4 volts or more.

While the form of embodiment of the inventon as herein disclosed, constitutes a preferred form, it: is to be understood that other forms might be adopted, as may come within the scope of the, claims which follow.

What is claimed is as follows:

1. The process of removing adherent rust from iron and steel surfaces. wh ch consists of immersingsaid surfaces for a suflicien-t length of time to remove the rust, in an aqueous solution consisting essentially of about 10 oz; of tetrasodium pyrophosphate per gallon of water and an acid sufiicient to reduce the pH value between 9 and 7.

2. The process of removing adherent rust from iron and steel surfaces which consists of immersin said surfaces for a sufiicient, length of time to. remove, the rust in an aqueous, solution consis in essentially of an aq eous. solution of tetrasodium pyrophosphate and an acid sufficient t reduce the. pH. value between'9 and'7.

THOMAS BURKHARDT.

REEERENCES CITED,

The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date,

1,572,848 Porter et a1 Feb. 9, 1926 2,093,927 Preston Sept. 21, 1937 2y 279,314 Henderson et. a1. Apr. 14, 1942 2,304,850 Rice Dec. 15, 19 42 FOREIGN PATENTS Number Country Date 253,554, Great. Britain Sept. 14, 1927 OTHER REFERENCES Soap, November, 1938, pages 24, 25, 26 and 26A. Soap, August 1939, page 59. Soap, January 1939, pages 24, 25, 26 and 69. 

1. THE PROCESS OF REMOVING ADHERENT RUST FROM IRON AND STEEL SURFACES WHICH CONSITS OF IMMERSING SAID SURFACES FOR A SUFFICIENT LENGTH OF TIME TO REMOVE THE RUST IN AN AQUEOUS SOLUTION CONSISTING ESSENTIALLY OF ABOUT 10 OZ. OF TETRASODIUM PYROPHOSPHATE PER GALLON OF WATER AND AN ACID SUFFICIENT TO REDUCE THE PH VALUE BETWEEN 9 AND
 7. 